• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1212-1217
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• 2004

Red organic electroluminescent (EL) devices based on tris(8-hydroxyquinorine aluminum) (Alq$_3$) doped with red emissive materials, 4-(dicyanomethylene)-2-t-butyl -6-(l,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB). poly(3-hexylthiophene) (P3HT). rubrene and 4-dicyanomethylene-2-methyl-6[2-(2,3.6.7-tetrahydro-lH,5H-benzo-[i,j]quinolizin-8yl)vinyl]-4H-pyran (DCM2) were fabricated for applying to the red light source, The photoluminescence (pL) intensities of red emissive materials doped in Alq$_3$ are limited by the concentration quenching with increasing the doping ratio and the doping concentration of DCJTB, DCM2, P3HT and rubrene measured at the maximum intensity showed 5, 1, 0.5 and 2 wt%, respectively. Time-resolved PL dynamic results showed that the PL lifetime of red emissive materials doped in Alq$_3$ were increased more than the value of material itself. It means that the efficient energy transfer occurred in the mixed state and Alq$_3$ is a suitable host materials for red emissive materials, The device which was used DCJTB as a dopant achieved the best result of the maximum luminance of 594 cd/$m^2$ at 15 V and showed the chromaticity coordinates of x=0,624, y=0,371.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.5
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• pp.859-870
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• 2020

The MQTT-SN (Message Queuing Telemetry Transport-Sensor Network) protocol is a message transmission protocol used in a sensor-based Internet of Things (IoT) environment. This MQTT-SN protocol is a publish-subscribe model with a broker in the middle of message transmission, and each IoT device sends and receives messages through an intermediary when delivering messages. However, the MQTT-SN protocol does not provide security-related functions such as message security, mutual authentication, access control, and broker security. Accordingly, various security problems have recently occurred, and a situation in which security is required has emerged. In this paper, we review the security requirements of MQTT-SN once again, and propose a modified protocol that improves security while satisfying the constraints in the environment where the resource of IoT to which this protocol is applied is limited. Unlike the existing protocol, the security field and authentication server have been added to satisfy the security requirements. In addition, the proposed protocol is actually implemented and tested, and the proposed protocol is evaluated for practical use in terms of energy consumption.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.2 no.1
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• pp.27-35
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• 1998

In this paper, we propose a novel spectral-chopping model of Class-II$(1+D)^2$ -PRS system which reveals improved spectral efficiency. We build up the model having spectrum chopped by the amount of Nyquist over-rate, and then compare its characteristics with the conventional model in both the time-domain and the frequency-domain. When the transmission system operates above the Nyquist rate, the new model has better performance than the conventional PRS using its inherent speed-tolerance. According to our investigations, Class-II PRS shows more excellent effect in the spectral-chopping method than Class- I and W types analyzed previously. We ascertain that the over-rate of 26.675 obtained by the inherent speed-tolerance could be improved upto 40% using spectrum-truncation. These effects come from the fact that the raised-cosine spectrum of Class-II PRS has smaller Boss of frequency component and energy than any other types for the same amount of truncation. In order to validate these theoretical results, we present their sidelobe-trends confirming cancellation effects at the sampling instants and some experimental results showing their patterns of eye-openings and spectra.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.5
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• pp.343-354
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• 2009

In this paper, a magnetic-less dc-dc switching converter realizing an integrable power conversion system is described. Instead of magnetic devices, the inductive impedance range of piezoelectric transducers is utilized to store and resonate the energy for soft-switching. Piezoelectric devices have no windings and deliver the power by the electrodes, which lead to mass product through semiconductor-manufacturing process. This paper presents a resonant-type step-up dc-dc power converter employing a disk-type piezoelectric transducer, analyzing the operation principles and the frequency control characteristics. Also, a topology extension of the single stage converter into cascaded multi-stage is presented and analyzed with the operation principles and control characteristics. For verification of the analysis, a 10W output dc-dc power converter hardware was implemented. The hardware experiments shows a good frequency control and power efficiency greater than 96% in the single stage. A hardware prototype of the extended multi-stage one was also realized and tested. The results shows that the converter has the same frequency control performance and high efficiency such as 93%.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.10
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• pp.773-778
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• 2012

A road energy harvester was designed and fabricated to convert mechanical energy from the vehicle load to electrical energy. The road energy harvester is composed of 16 piezoelectric cantilevers. We fabricated prototypes using a vehicle load transfer mechanism. Applying a vehicle load transfer mechanism rather than directly installing energy harvesters under roads decreases the area of road construction and allows more energy harvesters to be installed on the side of the road. The power generation amount with respect to the vehicular velocity change was assessed by installing the vehicle load transfer mechanism form and underground form. The energy harvester installed in the underground form generated power of 4.52 mJ at the vehicular velocity of 50 km/h. Also, power generation of the energy harvester installed in the vehicle load transfer mechanism form was 48.65 mJ at the vehicular velocity of 50 km/h.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1656-1658
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• 2003

고전압 대전류 시스템에 사용하는 스위치의 기본 요구조건은 저가, 긴 수명, 적은 지터와 대용량 그리고 seal-off 형태로 쉽게 설치하여 운전하는 것이다. 본 논문은 고전압 대전류용 Seal-off TVS (Triggered Vacuum Switch)를 개발하는 것을 목적으로 하고있다. 제작한 TVS는 양전극과 음전극이 교대로 고정된 간격으로 각각 3개의 전극으로 배열되어 있으며 전극은 사다리꼴 모양으로 되어있고 트리거 시스템과 개스를 흡수하는 게터가 내부에 설치되어 있다. 제작한 스위치 내부는 약 $10^{-7}$ torr의 진공상태를 유지하고 있으며 세라믹 챔버를 사용하여 Seal-off 상태로 설계, 제작하였다. TVS의 에너지 최고 전달량은 74 C 이며 30 kV, 100 kA, $1{\sim}2$ ms의 스위치를 제작하여 시험을 하였다. 스위치 시험 장치는 200 ${\mu}F$, 22 kV 6개를 병렬로 연결한 커패시터 뱅크와 160 ${\mu}H$의 인덕터와 0.2 ${\Omega}$의 저항을 이용하여 시험 장치를 구성하였다. 본 논문은 제작한 스위치의 전기적인 특성 시험한 결과에 대하여 논하고자 한다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.1
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• pp.25-33
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• 2008

Water waves are generated mainly by winds in open seas and large lakes. They carry a significant amount of energy from winds into near-shore region. Thereby they significantly contribute to the regional hydrodynamics and transport process, producing strong physical, geological and environmental impact on coastal environment and on human activities in the coastal area. Furthermore an accurate prediction of the hydrodynamic effects due to wave interaction with offshore structures is a necessary requirement in the design, protection and operation of such structures. In the present paper surface and internal waves scattering by thin surface-piercing and bottom-standing vertical barriers in a two-layer fluid is analyzed in two-dimensions within the context of linearized theory of water waves. The reflection coefficients for surface and internal waves are computed and analyzed in various cases. It is found that wave reflection is strongly dependent on the interface location and the fluid density ratio apart from the barrier geometry.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.151-157
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• 2002

화석에너지에 대한 경제적 부담과 환경오염문제를 줄이기 위하여 열펌프의 성능계수향상을 위하여 냉온 공기열교환기(HEEVA)를 고안하였고, 이 열교환기의 열특성과 성능계수향상에 미치는 영향을 분석하기 위하여 냉.난방 실험을 수행하였다. HEEVA에 의한 찬 공기와 더운 공기의 온도변화, 전열량 및 냉온 공기열교환기 효율, 총열전달계수등을 측정분석하였고, 냉난방시 외기온에 따른 열펌프의 성능계수, 소비전력, 응축기.증발기 출구 공기토출 온도 변화를 측정 분석함으로서 다음과 같은 결과를 얻을 수 있었다. 1. 외기온이 -4~11$^{\circ}C$로 변할 때 열펌프의 난방과정에서 HEEVA 찬공기 입출구 온도차는 4.5$^{\circ}C$에서 9.$0^{\circ}C$로 증가하였으며, HEEVA에 의한 영향으로 2~6$^{\circ}C$상승된 공기가 증발기 입구로 유입되어 냉매증발을 촉진하였다. 2. 실온이 4~22$^{\circ}C$일 때 HEEVA 더운공기 입출구 온도차는 3$^{\circ}C$에서 7$^{\circ}C$로 증가하였으며, 응축기에 유입되는 공기온도를 3~8$^{\circ}C$낮게 함으로서 압축기 소모전력을 감소시켜 COP 상승 효과를 나타냈다. 3. 외기온과 실온변화에 따라 풍량 346m$^3$/hr의 찬 공기가 받은 열량과 풍량 747m$^3$/hr의 더운 공기가 준 열량간의 차는 50~150kcal/hr로 나타났으며, 더운 공기가 준열량과 찬 공기가 받은 열량의 비가 83~98% 이었으므로 HEEVA의 열 교환율은 91% 을 보였다. 4. 총합열전달계수는 이론값이 실험 값보다 1~3W/m$^2$K 크게 나타났으며, 이 결과는 두 값 사이에 10% 내.외의 편차로서 Nusselt수를 구하기 위한 Petukhov상관식의 자체오차 15%에 비해 크지 않은 오차범주에 속하며, 이론상의 총합열전달계수 유도식의 타당성을 입증한 것이라 하겠다. 5. HEEVA를 작동함으로서 난방시 COP가 HEEVA를 작동하지 않았을 경우보다 0.3~0.5 향상된 것으로 나타났다. 이것은 HEEVA가 겨울철 난방에 효율을 높일수 있는 것으로 판단된다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.6
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• pp.1055-1059
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• 2006

In Wireless Sensor Networks(WSNs), a sensor node broadcasts the acquisited sensing data to neighboring other nodes and it makes serious data duplication problem that increases network traffic loads and data loss. This problem is concerned with the conflict condition for supporting both the reliability of data transfer and avoidance of network congestion. To solve the problem, a reliable congestion control protocol is necessary that considers critical factors affecting on data transfer reliability such as reliable data transmission, wireless loss, and congestion loss for supporting effective congestion control in WSNs. In his paper, we proposes a reliable congestion protocol, called HRCCP, based on hop-hop sequence number, and DSbACK by minimizing useless data transfers as an energy-saved congestion control method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.226-229
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• 2010

LED(Light Emitting Diode) is an emitting device which energy is same to the bandgap of p-type and n-type semiconductor junction. Recently high brightness LED is used in fish-luring light and traffic signal light alternative of normal light bulb, and widely used in the area of display pannel. Moreover nowadays LED has been used as a back light of LCD display. Recently, visible light communication(VLC) using LED, that allow two-way serial data communication between LEDs over a distance of sveral centimeters or meters, has been widely studied in the area of digital information transmission along with illumination and display. In this paper, we present LED communication system and their applications.